1. Field of the Invention
The present invention relates to a tread for a vehicle tire. In particular, the present invention relates to improvements to the tread of an all season tire and which improvements enable relatively long and relatively even wear of tread elements of the tire.
2. Background of the Invention
An all season type of tire is known in the industry. A typical all season tire includes a tread having relatively wide transverse extending grooves providing a plurality of discrete tread elements arrange in a circumferential array around the periphery of the tire. The relatively wide transverse grooves are necessary in order to efficiently evacuate water and snow from between a rotating tire and a ground surface.
The introduction of the relatively wide transverse grooves in an early all season tire gave rise to a relatively noisy tire. The relatively high noise generated by such a tire generally became objectionable to vehicle occupants. To correct the relatively high noise problem, tire designers began creating tread elements having different circumferential pitch lengths. By differing the circumferential pitch lengths, additive sound frequencies which created the objectionable noise are minimized.
However, the varied circumferential pitch lengths associated with the tread elements also possess varied stiffness characteristics. That is, each tread element of varied circumferential pitch length has a varied stiffness characteristic which resists movement of the tread element in the circumferential and lateral directions as the tire rotates through the contact patch.
Such differences in circumferential stiffness often causes irregular wear among the tread elements on the same tire. Furthermore, scrubbing, defined as the relative motion or movement between the tread surface and the ground surface at the interface between the tire and the ground, of each individual tread element is the principle cause of wear. This scrubbing phenomena often occurs with relatively large or stiff tread elements. Thus, improvements to reduce irregular and accelerated wear of tread elements, especially in an all season tire, are continually being sought.
Varying the number of sipes in a tread element has been done in previous tire designs primarily in order to compliment aesthetic features of the tire and give some improved traction in snow. Furthermore, these sipes were typically introduced to extend a radial depth which is less than the radial depth circumferential or transverse grooves.